Pathlength dependence of energy loss within in-medium showers

TL;DR

This paper investigates how the energy loss of in-medium parton showers depends on the pathlength within the medium, comparing model predictions with experimental data on hadron suppression relative to the reaction plane.

Contribution

It demonstrates the emergence of pathlength dependence in a Monte Carlo shower model and compares it to leading parton energy loss models and experimental results.

Findings

Model reproduces reaction plane dependence of R_AA.

Pathlength dependence in shower models aligns with leading parton energy loss.

Results support the use of in-medium shower models for jet quenching studies.

Abstract

Studying the pathlength dependence of high P_T hadron suppression in heavy-ion collisions by measuring the dependence of hard hadron production on the angle phi with the reaction plane in non-central collisions has so far been one of the most successful tools in constraining the microscopical picture of leading parton energy loss. With the imminent start of the LHC heavy-ion program and the possibility of full jet reconstruction, the focus has shifted to models which are capable of simulating full in-medium parton showers rather than tracing the leading parton only. Yet, on the level of single inclusive hadron observables, such shower models need to reproduce the findings of leading parton energy loss models, in particular they need to reproduce the correct reaction plane angle dependence of hadron suppression. The aim of this work is to illustrate at the example of the in-medium shower code YaJEM (Yet another Jet Energy-loss Model) how pathlength dependence arises in a MC shower formulation, how it relates to pathlength dependence of leading parton energy loss and how model results compare with data on the reaction plane dependence of the nuclear suppression factor R_AA(phi).